In ink-jet printing methods, droplets of ink are directly projected onto a printing medium from very fine nozzles and allowed to adhere to the printing medium to form characters or images thereon. The ink-jet printing methods have now been employed not only in printing applications for ordinary consumers but also recently in commercial and industrial printing applications because of various advantages such as easiness of full coloration, low cost, capability of using a plain paper as the printing medium, non-contact with printed characters or images, etc.
In addition, it has been required to print characters or images on a printing medium for commercial printing purposes such as a low-water absorbing coated paper such as an offset coated paper or a non-water absorbing resin film such as a polyvinyl chloride resin film, a polypropylene resin film and a polyester resin film.
In the commercial and industrial printing applications, it has been demanded to obtain printed materials with high productivity as compared to the printing applications for consumers. For example, there has been proposed the high-speed printing method in which a printing roll paper is scanned using a stationary print head of a ling head printing type.
For example, JP 2008-238485A (Patent Literature 1) discloses an ink-jet printing method capable of improving ejection stability of fine droplets of a water-based ink having a high content of a high-boiling aqueous solvent, in which the water-based ink includes a pigment and an organic solvent such as dipropylene glycol monomethyl ether and is ejected in the form of droplets each having a volume of not more than 3 pL from funnel-shaped nozzles arranged in a line print head.
JP 2006-298978A (Patent Literature 2) discloses a water-based ink set for ink-jet printing which is capable of forming black images by overstriking two different color inks as a water-based ink that is capable of clearly expressing black characters or line images with a high density and forming high-quality black gradation images, and is excellent in drying properties.
JP 2015-13990A (Patent Literature 3) discloses a water-based ink for ink-jet printing which includes specific water-insoluble polymer particles containing a pigment, another water-insoluble polymer particles and an organic solvent having a specific boiling point, in which a content of the organic solvent in the water-based ink is not less than 20% by mass, as a water-based ink which is excellent in optical density even when printed on any of a high-water absorbing printing medium and a low-water absorbing printing medium, spreading of a dot size of the ink on the low-water absorbing printing medium, and rub fastness.
In addition, JP 2015-85568A (Patent Literature 4) discloses as a printing method of obtaining good images that are free of bleeding and ensure solid image uniformity and rub fastness, an image printing method which includes a printing step of allowing an ink to adhere onto a non-porous printing medium whose printing side surface is adjusted to a temperature of 40 to 60° C., and a drying step of drying the ink adhered onto the printing medium, in which the aforementioned ink includes at least water, a water-soluble organic solvent containing no solvent having a boiling point of higher than 250° C., a colorant and fine resin particles, and in the printing step, a temperature of the surface of the printing medium is reduced as the number of scanning of the printing is increased.